Phenolic resins are useful compounds as hardeners for semiconductor-sealing epoxy resins, source materials for epoxy resins, adhesives, molding materials, and paints. Phenolic resins are widely used in electrical/electronic components, structural materials, adhesives, paints, and other fields, since cured phenolic resins have excellent electrical properties, heat resistance, adhesion, moisture resistance, and others.
Further, with advancement in the electrical/electronics field, semiconductor-sealing epoxy resins are required to have various properties such as high purity, heat resistance, moisture resistance, adhesion, low viscosity ensuring high filler content, low dielectric constant, rapid curing performance, and flame retardancy. In particular, lead-free soldering, which is introduced to meet environmental problems, requires soldering temperature higher than before, so that there is demand for improving adhesion between chips and frames composing IC and the sealing resin or adhesion between the filler and sealing resin to prevent separation or crack of packages.
In addition, because of the regulation on use of conventional bromine-containing flame retardants, the flame retardancy of the resin itself is also required to be improved.
In order to solve these problems, Japanese Patent Laid-Open Publication No. 2003-286392 describes a technique of improving adhesion of an epoxy composition by adding dibenzothiophene for prevention of cracks caused on packages by heating in reflow soldering process. However, since the above compound is quite inert and has a low boiling point of around 330° C., there are problems in heat resistance and flame retardancy.
Japanese Patent Laid-Open Publication No. H10-237060 discloses a technique of preventing package separation by improving adhesion using polyhydric phenols prepared through polycondensation between hetero aldehydes and phenols. However, production of these polyhydric phenols requires a long reaction time because of extremely low reactivity and has difficulty in producing high polymers. Also, the production involves many steps, such as neutralization of alkaline water and repeated washing of resulting salts, and generates a large amount of wastewater in neutralization and washing. Furthermore, there are a number of problems including slow curing speed of molded products and lowering in mechanical strength.
Phenolic resins are useful compounds as hardeners for electronic circuit board epoxy resins, source materials for epoxy resins, or the like. Since cured phenolic resins are excellent in electrical properties, heat resistance, adhesion, moisture resistance, and others, fiber-reinforced resin boards in which a phenolic resin is incorporated into a fiber base and cured to form a matrix, for example, laminates made of fiber-reinforced resin are widely used as electrical insulating materials or the like in the field of electrical/electronic components.
The fiber-reinforced resin board with phenolic resin matrix can be produced as follows: a fiber base is impregnated with a phenolic resin varnish in which a phenolic resin is dissolved in an organic solvent and the varnish is dried to prepare a semi-cured prepreg; a predetermined number of prepregs are stacked; and the resin is fully cured.
As examples of phenolic resins used for producing such fiber-reinforced resin boards, there may be mentioned resol-type phenolic resins. However, fiber-reinforced resin boards using resol-type phenolic resins have disadvantages of low electrical insulation and inadequate heat resistance. In order to resolve these disadvantages, Japanese Patent Laid-Open Publication No. H02-73824 proposes fiber-reinforced resin boards using various novolac-type phenolic resins as matrix. However, the boards were inadequate in flame retardancy, and addition of a bromine-containing flame retardant was required to impart flame retardancy to the resin composition.
Because of the European Union regulation on use of conventional bromine-containing flame retardants, the flame retardancy of the resin itself is also required to be improved.
On the other hand, as method for manufacturing multilayer printed circuit boards in place of the conventional laminating press process, there has been intensively developed so-called build-up process in which organic insulating films and conductive layers are alternatively laminated without glass fabric, which is disadvantageous in dielectric properties.
In the build-up process, a rubber component is sometimes added to enhance adhesion between the insulating layer and conductive layer. The rubber component remaining in the insulating layer, in some cases, deteriorates performances such as heat resistance and electrical insulation. Therefore, improvement in adhesion of resin itself is requested.